Microsoft blasted recent claims that the new TDL-4 botnet was indestructible. No botnet is impervious to decapitating C&C takedowns and a concerted attack, it states. (Source: Google Images)

Company points to takedown of "indestructible" Rustock, Waledac as case studies in how to kill a tough botnet

Today, networks of malware infected computers called "botnets" are controlled by malicious masters to spread spam and orchestrate takedown attacks across the internet. The botnets are growing very, very well crafted, leading some to suggest that they may be "indestructible".

In response to one such claim by Dell Inc. (DELL) SecureWorks research Joe Stewart, who said that the TDL-4 botnet was "pretty much indestructible", the senior attorney with Microsoft Corp.'s (MSFT) Digital Crime Unit argued that claim is false and that any botnet is destructible.

Richard Boscovich comments in an interview with ComputerWorld, "If someone says that a botnet is indestructible, they are not being very creative legally or technically. To say that it can't be done underestimates the ability of the good guys. People seem to be saying that the bad guys are smarter, better. But the answer to that is 'no.'"

TDL-4 will certainly be a tough. The malware has infected 4.5 million PCs thus far, and embeds a rootkit deep in the hard drive, in the master boot record. The malware removes other pieces of malware found on the machine to avoid detection. And it uses peer-to-peer connections to update its list of command and control (C&C) servers, safeguarding the botnet from takedown of C&C servers.

However, Microsoft takes major issue with the idea that TDL-4 is indestructible. After all, Microsoft already killed a botnet called "Waledac" that used similar peer-to-peer updates. Waledac, known for sending up to 1.5 billion pieces of spam daily, was decapitated in February 2010 when a court order allowed Microsoft to cut off 276 domains associated with the botnet.

Microsoft also used additional undisclosed measures (perhaps denial of service attacks) to make sure the peer-to-peer network was fully dead and unable to update the C&C information.

In March, with help from Microsoft, federal agents raided a hosting company, seizing servers responsible for the Rustock botnet. With the botnet brains decapitated, the botnet effectively died, taking half of spam in the U.S. with it. And in April Microsoft and federal authorities successfully killed the 10-year-old "Coreflood" botnet via a similar C&C decapitation approach.

Mr. Boscovich comments, "[Waledac] was a proof of concept that showed we are able to poison the peer-to-peer table of a botnet. Each takedown is different, each one is complicated in its own way. Each one is going to be different, but that doesn't mean that there cannot be a way to do this with any botnet."

However, even Dell backed off somewhat from their initial remarks, with a SecureWorks spokesperson saying this week, "Since mid-March 2011, Dell SecureWorks' CTU [Counter Threat Unit] research team has seen a significant decline in the number of attempted Rustock attacks, and we do attribute it to the comprehensive efforts of Microsoft."

Indeed Alex Lanstein, a senior engineer with FireEye, a security organization who worked with Microsoft on the takedowns says cooperation between Microsoft, other companies, and U.S. law enforcement agencies has proved integral to creating combined assaults capable of bringing down tough botnets. He states, "It's the trust relationships Microsoft has created and I think [the technique] speaks to any malware infrastructure where some kind of data feed exists. It really, really works. With the Rustock takedown, Microsoft has built the framework for others to do the same. This is definitely not the last botnet we're going to go after."

So, TDL-4 may be tough -- but "indestructible"? Not so much.

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"This is about the Internet. Everything on the Internet is encrypted. This is not a BlackBerry-only issue. If they can't deal with the Internet, they should shut it off." -- RIM co-CEO Michael Lazaridis